|25 June 2009
GSA Release No. 09-36
Director - GSA Communications & Marketing
JUNE 2009 LITHOSPHERE MEDIA HIGHLIGHTS
Boulder, CO, USA - The third issue of GSA’s newest journal, LITHOSPHERE, is now available online and in print. Papers cover CAT/SCAN seismic imaging in southern Italy that reveals a clear image of the subducting Ionian plate; details on low-angle normal faulting in the Aegean region, Greece; a paleomagnetic study of Tertiary intrusions in the northern Cerrillos hills, New Mexico, USA, contradicting previous study results; and what flysch deposits say about the geodynamics of Crete.
Highlights are provided below. Representatives of the media may obtain complementary copies of any LITHOSPHERE article by contacting Christa Stratton at the address above. Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to LITHOSPHERE in articles published. Contact Christa Stratton for additional information or assistance.
Non-media requests for articles may be directed to GSA Sales and Service, .
Imaging the subducted slab under the Calabrian Arc, Italy, from receiver function analysis
Nicola Piana Agostinetti et al., Istituto Nazionale di Geofisica e Vulcanologia, Centro Nazionale Terremoti, Via Vigna Murata 605, Rome 00143, Italy. Pages 131-138.
Piana Agostinetti et al. use data from the CAT/SCAN seismic deployment in southern Italy to reconstruct the crust and uppermost mantle structure across the Calabrian Arc, where the last fragment of the former Tethys Ocean is being subducted. They provide a clear image of the subducting Ionian plate at shallow depth where it bends and starts to descend into the mantle. The locus where the Ionian plate changes its dip and starts to subduct corresponds to the transition from an uplifted plateau to an extensional basin at the surface. It suggests that the Ionian plate has not rolled back relative to Calabria since it slowed.
Deformation and alteration of a granodiorite during low-angle normal faulting (Serifos, Greece)
Cornelius Tschegg, University of Vienna, Dept. of Lithospheric Research, Althanstr. 14, Vienna 1090, Austria; and Bernhard Grasemann. Pages 139-154.
Tschegg and Grasemann present detailed (micro)structural, mineralogical, and geochemical records of a granitoid pluton that during the Miocene (ca. 9 Ma) intruded into a major low-angle shear zone in the extension of the Aegean region in Greece. Comparison of the undeformed to the progressively sheared granodiorite allows identification and quantification of rock alteration, mass flux, deformation mechanisms, and displacement operating in an extensional shear zone, facilitating stretching and exhumation of rocks.
Paleomagnetism of Tertiary intrusive and volcaniclastic rocks of the Cerrillos Hills and surrounding region, Española Basin, New Mexico, U.S.A.: Assessment and implications of vertical-axis rotations associated with extension of the Rio Grande rift
Stephen S. Harlan, George Mason University, Dept. of Atmospheric, Oceanic and Earth Sciences, 4400 University Dr., MS 5F2, Fairfax, Virginia 20111, USA; and John W. Geissman. Pages 155-173.
The Rio Grande rift is a major intracratonic rift that separates the relatively thick and undeformed crust of the Colorado Plateau on the west from the Great Plains on the east. It extends from northern Colorado southward to where it merges with the eastern Basin and Range province of Arizona and northern Mexico. It consists of a series of north-trending basins and bound uplifts that are forming in response to crustal extension that is slowly ripping the North American continent apart. Accommodating the crustal extension and the pulling apart of the crust requires movement along basin-bounding faults and fractures. Most of the movement along the rift faults is down the dip of the fault plane as the crustal blocks are pulled apart. Recently, however, a number of studies have shown that some rotation of crustal blocks about a vertical axis is required to accommodate various degrees of extension along different parts of the rift. In the Espanola Basin of northern New Mexico, most of this vertical-axis rotation has been postulated to have occurred in a counter clockwise sense. In this study, researchers from George Mason University and the University of New Mexico have conducted a paleomagnetic study of Tertiary intrusions in the northern Cerrillos hills in order to test this hypothesis. Their results show that despite the evidence for crustal extension in the Espanola Basin, the amount of vertical axis rotation that accompanied rifting is significantly less than has been previously estimated and may be negligible. This result contradicts results of other studies that suggest that counterclockwise crustal rotations may be an important component of recent rift extension and deformation.
Calcite twinning strains in Alpine orogen flysch: Implications for thrust-nappe mechanics and the geodynamics of Crete
John P. Craddock et al., Macalester College, Geology, 1600 Grand Ave., St. Paul, Minnesota 55105, USA. Pages 174-191.
Flysch is a type of marine sediment that forms adjacent to mountain belts in shallow foreland basins. In Crete, during the Miocene, mountains similar to the Alps began uplifting and, as the mountains formed by horizontal motions on north-dipping thrust faults, the flysch deposits were squeezed between thrust sheets. In Crete, this relationship is well exposed; the ages of the flysch deposits constrain the ages of fault motions and reveal the style of deformation that formed the Alps.
View abstracts for the complete issue of LITHOSPHERE at http://lithosphere.gsapubs.org/current.dtl.